1880.] 1^^ [Haupt. 



and it is situated at a point where its effects might have been considered 

 "altogether insufficient, uncertain and ill-defined." 



(The cut is reproduced from Prof. Hilgard's paper, Smithsonian Report, 

 1874, page 221.) 



The accompanying letter, recently received from Prof. Hilgard, is con- 

 clusive as to the probable efficiency of these plans : 



"1349 L St. 

 "Washington, May 20, 1888. 



"My Dear Prop. Haupt : I have received your interesting paper on 

 the 'Physical Phenomena of Harbor Entrances,' in which you describe 

 the peculiar forms of the bars and spits found at the inlets along the sandy 

 cordon of islands defending the Atlantic coast line and give your explana- 

 tion as to the forces producing them ; ascribing them chiefly to the energy 

 of the flood tide as afiected by the general form of the coast line. 



"In this I think you are entirely correct, as it is undoubtedly the un- 

 ceasing activity of the flood that produces the forms which are so charac- 

 teristic of harbor entrances, and not the wind waves produced by prevail- 

 ing winds. The direction of motion of the beach sands is, as a rule, the 

 same as that of the flood tide along the shore. It is modified by great 

 storms, but only temporarily, and in a short time the flood reasserts its 

 supremacy and the channel returns to its normal position. 



"In applying this physical fact to the plans for improving the bars, I 

 believe you have proposed the best form to resist the encroachments of 

 the sand and yet admit the flood tide freely. These are fundamental condi- 

 tions, and you have fully met them while providing at the same time 

 ample facilities for navigation. 



"The successful operation of your proposed plan is well illustrated by 

 the accidental experience with the stone fleet on Charleston bar, described 

 in my paper on ' Tides and Tidal Action in Harbors,' published in the 

 Smithsonian Report for 1874. From that instance it is seen that by ob- 

 structing tiie inflow of sand and Inducing an ebb current, two good chan- 

 nels were formed, the better one to the leeward of the obstruction. Your 

 plans would change the conditions of equilibrium in favor of the ebb, and 

 the length of your breakwater is much less than that required by existing 

 methods. 



"I trust that they will be tried at some suitable entrance along the At- 

 lantic or Gulf coast. 



"Yours, with great regard, 



"J. E. Hilgard. 



"Prof. Lewis M. Haupt, University of Pennsylvania." 



The eS"ects to be anticipated from the shore flank of the breakwater are 

 best instanced by those found at the Delaware breakwater, where a 

 straight barrier of half a mile in length stands at such an angle to Cape 

 Henlopen as to have been originally tangent to it when projected in 1828. 

 Its end is about a half mile from shore, and it is open to the north-west 



